There is no such advantage or disadvantage between 5 sensors and 3 sensors. It's most likely different people's preference. Typically, 3 sensors will make the car work good enough as long as the inductor you choose will have signal overlap to each other.

What's the difference (advantages) of choosing 5 sensors over 3 sensors for natcar?

If you are talking about 3 front and 2 back, there MAY be an advantage because of being able to calculate directly the angle the car makes with the wire (instead of having to take the derivative). We've never tried 5 sensors in any configuration, so it's hard to say definitively.

I do know this: the Automated Highway System Demo '97 with 8 Buick LeSabres in a platoon on the I-15 freeway in San Diego had 6 magnetic sensors, 3 front and 3 rear, and they were perfectly reliable and effective. I have a vid of that if you want to see it.